Kawasaki disease is an acute febrile illness characterized by the inflammation of blood vessels, or vasculitis, throughout the body. It primarily affects children under the age of five, making it the most common cause of acquired heart disease in this age group in developed countries. Children often present with a prolonged high fever lasting more than five days, a widespread red rash, and swelling of the hands and feet. Other common symptoms include red eyes, very red lips and tongue, and enlarged lymph nodes in the neck. Despite extensive research, the exact cause of Kawasaki disease remains unknown.
The Role of Infectious Triggers
Evidence suggests Kawasaki disease is triggered by an infectious agent, though no single bacterium or virus has been consistently identified as the direct cause. The disease presents with infection-like symptoms, such as a persistent high fever, swollen lymph nodes, and a rash. It also exhibits distinct seasonal peaks, most commonly in late winter and early spring, and has been observed in community-wide outbreaks.
Researchers hypothesize the illness might be an unusual immune reaction to a common, otherwise harmless pathogen in certain children. Studies have explored correlations between Kawasaki disease outbreaks and specific respiratory viruses like rhinovirus and respiratory syncytial virus, as well as varicella outbreaks, noting significant correlations one to three months prior to Kawasaki disease peaks. However, the disease itself does not spread from person to person. This suggests that while an infectious trigger may initiate the process, the disease’s development is not simply about direct transmission.
Genetic Predisposition
Not every child exposed to a potential infectious trigger develops Kawasaki disease, indicating a genetic component influencing susceptibility. This genetic link is evident in the higher incidence among children of East Asian descent. For instance, children of Japanese and Korean ancestry experience the disease at rates 10 to 20 times higher than Caucasian children.
Siblings of a child diagnosed with Kawasaki disease also face a much greater risk of developing the condition compared to the general population, with this elevated risk being as much as tenfold higher. The current understanding suggests that certain individuals may possess specific genes that make their immune system more prone to an exaggerated response when exposed to an environmental trigger, leading to the characteristic inflammation seen in Kawasaki disease.
The Body’s Immune Response
The prevailing scientific understanding combines the influence of an infectious trigger with genetic susceptibility to explain the disease mechanism. In genetically predisposed children, an encounter with an infectious agent can set off an exaggerated immune system response. This system mistakenly targets the body’s own medium-sized arteries.
The primary focus of this misdirected attack is often the coronary arteries, which supply blood to the heart. This immune system assault causes widespread inflammation, or vasculitis. Atypical activation of immune cells like monocytes and macrophages is thought to initiate these vascular lesions. The inflammation can damage the collagen and elastic fibers within vessel walls, leading to a loss of structural integrity.
Environmental Clues and Ongoing Research
Beyond infectious triggers and genetic predispositions, environmental factors also offer clues to the cause of Kawasaki disease. The disease exhibits distinct geographical and seasonal patterns not fully explained by infection alone. For instance, seasonal peaks in Japan, Hawaii, and San Diego show a nearly synchronized pattern from November through March.
An interesting theory links large-scale wind patterns to the spread of a potential trigger. Studies suggest an airborne toxin or antigen, possibly fungal particles like Candida species from agricultural regions in northeastern China, could be transported by wind to Japan and across the North Pacific. This hypothesis implies a non-living trigger that causes an immune reaction in susceptible children. Research continues to investigate these interactions, acknowledging that the cause of Kawasaki disease is likely multifactorial.